Review SoundPrism Excellent Floating active loudspeakers: turning disadvantage into progress


Those who work in a small and traditional way, like Etienne Heemskerk of SoundPrism, sometimes manage to turn a potential bad situation into an advantage and improvement by other means. The result here is a sound reproduction that is calmer, more natural, gives a greatly improved stereo image, does not compromise on quality and turns listening to music into an even greater form of pleasure.


  • Turns listening to music into a celebration
  • Customisable to customer needs
  • New AMT tweeter earns extra points
  • Artisanal
  • Active and with DSP possibilities
  • Delivered and tuned at your premises
  • Favourable price tag in relation to the sound quality offered


  • Quite large, especially with 15" subwoofers
  • Requires a lot of wiring
  • Finish: form follows function

Shit happens. The active loudspeaker system developed by SoundPrism was partly unique because of the use of an AirBlade tweeter, however the manufacturer stopped supplying the tweeter because of production problems. The only option left was to use another tweeter brand and redefine the upper half of the system. Praise to SoundPrism owner Etienne Heemskerk not to throw in the towel, as he even managed to turn the initial disadvantage into an improved sound quality. The SoundPrism Excellent Floating loudspeaker system is a further development with more potential. A renewed visit to the manufacturer was therefore more than appropriate. On my way to Heerhugowaard in the Netherlands, where ears were opened and washed out! For Dutch, click here

SoundPrism: A short retrospect 

For anyone that has not read our article of the previous session, we will give a brief summary. Hidden in the North Holland town Heerhugowaard is the audio domain of Etienne Heemskerk. Under the name SoundPrism he designs and manufacturers fully active loudspeakers, for which the customer might deliver important input in the appearance, even in the applied electronics and the shape of the (sub)woofer. SoundPrism does not aim for serial production or selling large quantities of loudspeakers, the customers satisfaction and the aftercare offered by SoundPrism prohibits. Working small scale, determining the best solutions together with the client and subsequently tuning a system to size, is what appeals to Etienne a lot more. A representative system can be auditioned at SoundPrism's home town or at one of his dealers.

SoundPrism was not born out of an impulse by Etienne Heemskerk. His roots lie within the classical music he grew up with, playing the flute. He has made recording of soloists, orchestras, choirs and jazz musicians for a long time now, using a ribbon microphone system he designed and put together himself, using TritonAudio active preamplifiers, set up in an arrangement that often deviates from the usual choices. Only two microphones are in use, set up straight ahead next to each other, exactly the way our ears are positioned. The recordings are saved as digital files and not, or as little as possible, edited.

Grabbed by music Etienne has always had an interest in loudspeakers and electronics, at an early stage he chose active filtered loudspeakers, for perfect time coherence and minimal phase errors. Etienne sees himself as a builder of custom made loudspeakers, not as a manufacturer with serial products. His systems evolve, in such a way that a customer can grow along with the adjustments made. Mainly in progress of filter software, not in upgrading the units on the baffle unless necessary. It should also be mentioned that SoundPrism can be called upon for tuning audio and AV systems, converting passive loudspeakers into active, or modifying loudspeakers.

SoundPrism Excellent Floating

The Excellent Floating loudspeakers follow open baffle principles for the midrange and high frequencies. The baffle may be of any material, wood, MDF, plastic or even stone and finished in any way desired by the client. The baffle accommodates two Purifi woofers and a Mundorf AMT tweeter in a D'Appolito arrangement. The Purifi woofers use outstanding surrounds, optically shaped in a way when viewed from a distance they look damaged. It is a woofer from the Purifi design group of technicians, a company better known for the further development of Eigentakt class D amplifiers. The frequency range of the 6.5" woofer is almost flat from 100Hz to 3,000Hz and that makes it an ideal midrange unit in an open baffle. Crossover frequencies used are around 120 and 2800Hz.

The tweeter situated between the woofers is a Mundorf AMT. An Air Motion Transformer has a membrane of folds to transform the electrical energy for high frequencies into sound, like an accordion. The sound is squeezed out between the folds at high speed. The Mundorf AMT, unlike the AirBlade, does not have a 180 degree front to back radiation, but is limited to 60 degrees at 15kHz, still it is a dipole. You can literally look through the tweeter to the wall behind the baffle. Mundorf uses Neodymium for strong magnetic fields.

During the previous visit the baffle was mounted on a subwoofer, decoupled by dampers. This time Etienne has chosen to hang the baffle from the ceiling on steel wires. Two springs decouple the steel wire from the baffle. The weight of the baffle itself, with its three units, is enough to keep it stable, while the springs help to further minimise resonances or the passing on of mechanical energy. Both ways, from baffle to ceiling and vice versa. The reason to add “Floating” to the origin of the name SoundPrism Excellent. It is still possible to position the baffle in a frame, but even then a spring construction will completely decouple the baffle from the frame and the surface.

As should always be the case with an open baffle, the energy dispersed on the front and rear is the same, which is why a distance to the rear wall is necessary. Ideally, the speakers might be positioned in a room en suite, in between the two rooms. An open baffle ensures perfectly symmetrical loading for the drivers, prevents resonances, brings down distortion and cannot suffer from cabinet colouring. Efficiency is higher compared to closed systems, where energy is partly converted into heat within an enclosure.

The woofers SoundPrism uses in the setup in front of me are modified, passive, 15-inch Klipsch subwoofers. The electronics in the subs have been bypassed and the damping has been adjusted. On request and in consultation with the client, a smaller sub can be used, or from another brand, if space is limited one central sub between the two baffles might be enough. The subs are preferably placed on spring-loaded dampers to decouple them from the floor. Decoupling often proves to be much more effective than coupling with spikes. The dampers are Neolevs by TritonAudio, a company from Alkmaar in the Netherlands Etienne often deals with.

To build an active system, an electronic crossover and a power amplifier for each unit is required. SoundPrism uses a 3-channel electronic crossover from Hypex. The filter adjusts frequency, time delay, phase and more. Using a PC, the generated files are loaded into the filter using a USB connection. SoundPrism has three fixed settings, available by remote control, that way the client can choose which setting appeals most to him. The system is measured at the customer's home and optimised for the chosen settings, the cure for a number of acoustic problems in listening rooms, solved by means of DSP. Each filter channel uses a Purifi Eigentakt class D amplifier, directly coupled to the unit. Each Eigentakt is powered by a Hypex power supply and mounted in an enclosure as a two-channel amplifier. What remains for the customer is to connect an analogue source with volume control to the crossover. SoundPrism uses a Sonnet Audio Hermes streamer with Volumio software and a Sonnet Audio Morpheus DAC. A proven and delightful combination.

The SoundPrism Excellent Floating loudspeaker system is offered on the basis of a quotation, in which the wishes of the customer are included for the design and the subwoofers. The complete system includes the open baffles with Purifi and Mundorf units, two modified Klipsch 15 inch subwoofers, the Hypex filter, three complete Purifi Eigentakt stereo power amplifiers, cabling, installation, tuning and after two weeks fine tuning the system. The price starts at € 18,000 and only increases if case of special wishes that justify an additional price tag.

Past and present

During and after my previous visit, the SoundPrism active loudspeaker system left the impression of being a very fast transducer, honest and pure, with a wide, even balanced frequency range. It was an overwhelming system, enjoying music was at times like riding a roller coaster due to the AirBlade tweeter. The Mundorf tweeter exhibits a quieter behaviour, without sacrificing transparency or speed.

The smaller beam angle fits the Purifi midrange units in D'Appolito alignment even better. The concurrent radiation behaviour between the three units corresponds very well. The less aggressive Mundorf AMT hardly suffers from ringing compared to the AirBlade and because of the bundling in the treble range, reflections from side walls are less present, reason why a more stable stereo image is achieved. The two subs were set very smooth at the previous visit, this is still the case although they seem to play tighter now. Perhaps my memory is failing me on that point. Seated on the hotspot of the speaker system I start listening. Speakers placed 3.2 metres apart, measured at the centre of the baffle, listening distance is approximately 2.5 metres. The baffles are not angled towards me, units 'look' to a virtual point behind me.

Using my own text from the previous visit and my memories, I try to distinguish what is actually different now in the SoundPrism Excellent Floating system. To do so, I use previously played tracks and start with Stacey Kent's "The summer we crossed Europe in the rain". I am quickly convinced, the sound image has become calmer, listeners are not walking on tiptoes anymore. The image offered has become more natural, pays less attention to hi-fi characteristics and more to music. Music has not become boring or dead, on the contrary, a sizzle on the voice is still there, should be there, but now less pronounced. The focus is way better than expected, the stereo image free from the baffle and widely spread. There is a continuous, clear separation between instruments and the voice in the stereo image with ample attention to depth. The speed was not compromised either. Detailing is very good, especially in the very important midrange, where the doubling the number of the Purifi units and the D'Appolito set-up absolutely pays off. Beautifully has become the mildness of the tweeter and the inaudible crossing over between the various units. Two 15" subwoofers perform tight and straight, without any exaggeration, fitting in seamlessly with the baffle and together forming the foundation under the music.

With every piece of music I listen to I become more and more convinced; thanks to the Mundorf AMT and the double Purifi units, I am able to listen for a longer time than was the case with the AirBlade. Music plays invitingly, relaxed and has that nice character that draws the attention to the music and not always to the technique. Take for example Youn Sun Nah with "My favourite thing". Notes originating from the small instrument held in front of her belly, resonate for a long time. Larded with warmth and a richness of sound.

For the first time, I notice the intense vibration in her voice. It is so striking that a small, devilish voice whispers to me that the springs on the baffle work as reverb springs. Listening to the same track at home makes mincemeat of that devilish idea, the vibrating is still there, it was just never so obvious. This is due to the extraordinary intelligibility, the dead silence behind Youn Sun Nah, in combination with the total silence at the sides. The reproduction is dynamic and tones fade away very slowly until only silence remains. The whole system is focused and is as transparent as a full range electrostatic speaker.

Push the woofers to work with "Avratz" by the Israeli duo Infected Mushroom. The sound stage is very wide in this setting, reaching far beyond the physical arrangement of the speakers. The image is tight, perfectly controlled, to the point and fast. While sounds disperse, the bass is at first kept central by Infected Mushroom. Firm and yet with full control. All those little sounds are playful and lively, even though they are sometimes very softly recorded and threaten to melt away. The sound is never technical, just smooth and intense in the right way.

Tones can again really persist for a long time against a quiet background. The bass goes deep, no hump to be found and yet no DSP is used other than for crossover and phase correction. The impulse behaviour is excellent with the Klipsch subs. Only big woofers can pass on energy effortlessly, while small woofers have to work a lot harder and show a "pushing" behaviour.

Etienne's recordings

As mentioned, SoundPrism often makes its own recordings, including those of the Artvark saxophone quartet. Each member of the quartet has its own place in the playback, they are not compressed. Each member has a clearly identifiable place in depth, height and width of the sound stage.

It is a beautiful recording, made by Etienne himself, without audiophile flapping noises coming from the instruments. Very precise due to the use of a single stereo microphone. The pure sound of the four saxophones is preserved and this is combined with considerable dynamic peaks. The SoundPrism Excellent Floating follows the instruments effortlessly and without compression. The dual midrange units help to keep the reproduction free from the baffles while maintaining a strong focus due to the D'Appolito arrangement. The bundling of midrange units and tweeter is correct, thus avoiding phase problems.

Within the Nederlands Kamerkoor (Dutch Chamber Choir), voice by voice is identifiable. In between singing, a clear stumbling of feet can be heard in the background. I myself would not buy this music, it does not or hardly appeal to me. However, the reproduction is spectacularly good and detail enriched. With a natural sound. Even the turning of the sheet music is retained in the recording. A second piece combines electric guitar with choral singing. Voices soar and then the distorted guitar crackles like a dissonant. Think of a mix of Led Zeppelin and a church choir. The evil and the good, the darkness and the light. Definitely intriguing and very special demo music to demonstrate the quality of the SoundPrism Excellent Floating system.

Spectacle with the "Overture 1812", of which during the last 5 minutes fierce strings set the pace, brass players bulge their cheeks without becoming shrill, a choir stands wide spread behind the orchestra. Then kettledrums thump, a glockenspiel rings out. All this is realistically presented in an overwhelming grandeur. Wide, very wide in space and no loudspeaker can be heard as an entity. The good recording yields an exceptional result. What I never noticed before, and what may be related to especially this recording, is the firing of the cannons. But in a way that canon by canon is identifiable in the arrangement. Left, right, left right, shifted as they form a line. That is pure spectacle!

High volume levels with SoundPrism Excellent Floating are no problem, listen to the cracking French voice of Renaud, joined by harmonica and guitar. Recorded very loudly and with Renaud being close to the microphone. Therefore very direct. It is worthy of a PA system and is strongly reminiscent of music at a village festival on a French market. Nevertheless, the sound image remains balanced and Renaud sings about "Dylan" with total dedication and energy.

Turned into advantage

When the supplier of one of the most important components in your system lets you down, whether deliberately or unintentionally, you have a problem as a big manufacturer. Those who work in a small and traditional way, like Etienne Heemskerk of SoundPrism, sometimes manage to turn the situation into an improvement by other means. The SoundPrism Excellent Floating system is the result of the forced choice for another tweeter, whereby the decision was made towards a Mundorf AMT. The deployment of the new tweeter, in addition to doubling the number of midrange units forming a D'Appolito arrangement, was his first further development. Suspending the baffle to the ceiling, or in a frame when necessary, is a follow-up.

The result is a sound reproduction that is calmer, more natural, gives a greatly improved stereo image, does not compromise on quality and turns listening to music into an even greater form of pleasure. SoundPrism Excellent Floating is a complete, active system that lacks only a source and volume control. Furthermore, it includes all cables and accessories. Tuned, adapted to the client's wishes, delivered on a customised basis. The fact that it is too much handiwork to deliver in series may be a reassurance for larger manufacturers, otherwise SoundPrism Excellent Floating would be a formidable competitor for established names with considerably higher pricing. I cannot reward SoundPrism an even bigger compliment.